I had a "Mad World", but sold it last Spring. There's some debate as to whether it's a true multi-ball game or not, since the extra ball is not released onto the playfield. It can be immediately shot into play, but it's really just a free ball.

IT just requires a manual plunge assist onto the PF.

The first multiball game Balls a Poppin,
balls are released from under the playfield or wherever they are stashed;
unlike other early EM multi-ball games that have balls locked or captured then released onto the PF
without need of a plunger.
Some Modern games release multiballs (onto the PF) via an auto plunger.

I am in for Big Valley as well: 3" flippers plus multiball are just a fabulous combination!

Fireball

Fireball. The game can be maddening, but the multi-ball feature is brilliant, along with its artwork.